<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        /* div {
            display: flex;
        } */

        header {
            float: left;
            width: 200px;
            height: 100vh;
            background-color: aqua;
        }

        aside {
            float: left;
            /* 计算属性 calc() 运算符中间是空格 */
            width: calc(100% - 400px);
            height: 100vh;
            background-color: yellow;
        }

        footer {
            float: left;
            width: 200px;
            height: 100vh;
            background-color: aquamarine;
        }
    </style>
</head>

<body>
    <div>
        <header>1</header>
        <aside>2</aside>
        <footer>3</footer>
    </div>
</body>

</html>